Linked Data is the core technology enabling future library systems and the semantic web.
Libraries and cultural heritage organizations are shifting from MARC21 and XML metadata standards to Linked-Data vocabularies. Library Linked Data is an international effort to bring machine-readable data to the web. Based on RDF (Resource Description Framework) graphs, Library Linked Data is made up a series of statements, called triples, that take the form of subject - predicate - object.
A graph data structure is made up nodes (also known as vertices or points) with connections between the nodes called edges or directed edges (also referred to as arcs or lines)
Graphs are used to describe transportation systems, computer networks, and social relationships. Graphs easily support heterogeneous environments with different vocabularies that can scale to billions (if not trillions) of nodes and edges.
Linked Data in libraries is constructed using Resource Description Framework (RDF) graphs, a type of directed graphs, where the nodes are made up of either IRI (international resource indicator i.e. URLs or URIs), blank nodes (a type of identifier placeholder in a RDF graph), or literal values. Originating with the World Wide Web Consortium (W3C) specifications, RDF graphs are built using three element statements called triples that model relationships between resources, IRIs, and descriptive information.
In a RDF triple, the first element is called a subject and represents a resource with the second element, the predicate, describing an aspect that connects to the third element, an object made up a value, blank node, or IRI. One or more these triple statements make up a RDF graph.
The real power of RDF Linked Data comes when it is paired with a Triplestore that supports the RDF query language, SPARQL (short for SPARQL Protocol and RDF Query Language), allows for sophisticated retrieval of data within the triplestore as well as an means to manipulate the data by adding, editing, or deleting triples contained in the triplestore.
With RDF Linked Data coupled with SPARQL as enabled technologies for the "Semantic Web" a term initially created by Sir Tim Berners-Lee to describe web resources with a set of actionable metadata by algorithms and other machine processing.